Streptomyces lividans has been shown to have a potential as a microbial system useful for the efficient expression of heterologous proteins. S. Chang and S. Chang, "Secretion of Heterologous Proteins in Streptomyces lividans," Biology of actinomycites, 1988, Y. Okamia, T. Bepper, and Ogawara, Eds. (Japan Scientific Societies Press, Tokyo, 1988). However, heterologous protein expression is limited in some microbial systems, such as S. lividans, because of protein instability.
In an effort to increase yields of proteins expressed and secreted by bacteria, changes in content of the fermentation media have been explored. The effects of various chemically defined medium changes on the production of extracellular proteolytic activity has been explored for non-recombinant S. aureofaciens. C. LaLuce and R. Molinari, "Selection Of A Chemically Defined Medium For Submerged Cultivation of Streptomyces aureofaciens With High Extracellular Caseinolytic Activity," Biotechnology and Bioengineering, Vol. XIX, 1863-1884 (1977). In LaLuce et al., various amino acids were used as nitrogen sources, some increasing the production of proteases while others decreased the production of proteases.
Yields of heterologous proteins expressed from recombinant strains such as S. lividans TK24, are sometimes reduced by the action of proteases. Werner Aretz, Klaus P. Koller and Gunther Riess, "Proteolytic Enzymes from Recombinant Streptomyces lividans TK24" FEMS Microbiology Letters, 65:31-36 (1989). Aretz et al. discloses the addition of metal ions to the culture medium to inhibit certain proteases thereby increasing the yield of heterologous proteins.
Other attempts to define media effects on the expression of a heterologous gene are taught by Philippe Dehottay et al., "Cloning and Amplified Expression In Streptomyces lividans Of A Gene Encoding Extracellular .beta.-lactamase From Streptomyces albus G, " Gene, 42:31-36 (1986).
Casamino acids have been used to supplement microbiological media. Casamino acids have been shown to function as a growth promotant in non-recombinant yeast when added to a medium devoid of casamino acids. J. R. Ludwig II, S. G. Oliver, and C. S. McLaughlin, "The Effect Of Amino Acids On Growth And Phosphate Metabolism In A Prototrophic Yeast Strain," Biochemical and Biophysical Research Communications, Vol. 79, No. 1, 16-23 (1977).
A repressive effect of casamino acids has been demonstrated on exoprotease production in early phases of fermentation of Pseudomonas aerugenose. Michael A. Whooley, John. A. O'Callaghan and Aiden J. McLoughlin, "Effect Of Substrate On The Regulation Of Exoprotease Production By Pseudomonas aerugenosa ATCC 10145, " Journal Of General Microbiology, 129(4) 981-988 (1983).
In comparison, E. Strydom et al., in "Detection And Characterization Of Extracellular Proteases in Butyrivibrio fibrisolvens H17C," Appl. Microbiol. Biotechnol, 24:214-217 (1986) demonstrated protease production was maximal on a medium with casamino acids. Similarly, a tryptic digest of casein was shown to increase proteolytic activity in E. chrysanteoni. C. Wanderman, T. Andro and Y. Bertheau, "Extracellular Proteases in Erwinia chrysantemi," Journal of General Microbiology, 132:899-906 (1986). Additionally, casamino acids added to a complete medium increased protease production from Vibrio gazogenes. C. Ratcliffe et al. "Amylase and Protease Secretion By The Marine Bacterium Vibrio gazogenes," A.J. Biol. Sci., 35:457-67 (1982).
A variety of complex medium formulations, some including casamino acids, improved product production from recombinant yeast. S. J. Copella and Prasad Dhurjati, ".alpha.-Factor Directed Expression Of The Human Epidermal Growth Factor In Saccharomyces cerevisiae," Biotechnology and Bioengineering, 33:976-83 (1989). The addition of the combination, glucose and casamino acids to a totally defined medium where E. coli must synthesize, among others, amino acids, vitamins and nucleotides, increased the production level of a heterologous protein. G. K. Whitney, B. R. Glick and C. W. Robinson, "Induction of T4 DNA Ligase In A Recombinant Strain Of E. Coli, " Biotechnology and Bioengineering 33:991-998 (1989). During the terminal phase of cultivation, the addition of a water soluble alcohol and/or amino acid mixture has been demonstrated to improve the yield of a heterologous protein such as IFN-alpha, IFN-beta and IL-2 produced by recombinant bacteria. U.S. Pat. No. 4,656,132.
Casamino acids have also been shown to decrease the yield of a recombinant protein in a strain of Streptomyces. T. Erpicum et al., "Enzyme Production by Genetically Engineered Streptomyces Strains: Influence of Culture Conditions," Biotechnology and Bioengineering, 35:719-726 (1990).